The growth of the Internet over the past decade has provoked a tremendous rush to adoption of web sites by almost every company doing business today. This rush has included both internal (Intranet) presence as well as external (Internet) based presence. These myriad web sites each face the problem of web migration individually, so one company may have to tackle the challenge of web migration once for each unique environment it has built and supported.
The problem has to do with the rapid change of technology. By the time a large web site is complete it quickly becomes outdated. In the intervening years since web sites are built and deployed, technology continues to march forward while both static and dynamic web sites are frozen in time and lag behind. Sites are often trapped by the inability to make large-scale changes without impacting stability and customer satisfaction.
In short, once a web site is built and deployed, keeping up-to-date on upgrades (both software and hardware), the latest technologies, business process, etc., has meant a compromise between risking changes that might lower customer satisfaction or taking an extremely time-consuming and drawn out process that requires enormous personnel resources and devotion to quality assurance.
In fact, web migration is quickly becoming one of the most important and costly challenges facing any business with a web presence.